As the title states I'm chasing a very annoying fuel issue currently. Heres some info on the setup first
1987 Transam with a 5.3 LM7, stock return style rail regulator bypassed in favor of an aeromotive FPR, -8an fuel lines, walbro 525 hellcat fuel pump, deka 80# injectors. On3 7665 turbo set to 10psi. Car runs on e85.

The issue is when I start to reach about 4000RPM and get past about 5psi of boost, I drop fuel pressure substantially. Very quickly it leans out and goes from 45-50psi down to 30psi or even less. The ENTIRE fuel system is completely brand new save for maybe 100 miles put on all of it, and the filter isnt too old. The thing that puzzles me is that it wasn't doing this at first. When it was first on the dyno it did pulls just fine with no cutting up and then suddenly after 3/4 runs this began. Im tempted to pull the sending unit (also brand new) and check to see if something is awry inside the tank while running, but figured I would ask here first. Thanks!

 

How are you supplying power to the pump? I'm not familiar with that particular pump, but anything larger than a 255 walbro typically requires larger gage wiring to the pump. The stock wiring cannot supply the power loads most pumps require.

 

It did the first 3-4 pulls fine but after is when it started acting up so I dont think power is the issue but maybe. I'll look into it

 

On the Dyno you also don't get the aero loads as driving on the street. Your pump may have been just barely adequate on the Dyno but not enough to overcome aerodynamic loads on your car.

 

the issues began on the dyno

 

E85 is kind of a fuel tank cleaner. Your fuel system might be plugging up with contaminants. And not just the inline filter, but possibly the sock inside the tank too.

What fuel filter are you using?

How is the fuel regulator plumbed, including manifold pressure reference?

How is the fuel pump wired? Be very specific.

 

I bet your tuner was adjusting fuel tables after each run. Now the tune is commanding fuel from a fuel system that is not powered to handle it. Just a hunch.